ABSTRACT

The Pennsylvanian strata in the southern Canadian Rocky Mountains and Foothills are subdivided into five formations which in ascending order are: Todhunter, Tyrwhitt, Storelk, Tobermory, Kananaskis. The Tyrwhitt, Storelk, and Tobermory Formations are new and their type sections are located on Storelk Mountain in the Elk Mountains, B.C. The Todhunter, here elevated from member to formation rank, is a thin unit composed of sandstone, dolomite, limestone and siltstone that is transitional between the late Mississippian (Chesterian) Etherington Formation dolomite and limestone strata, and the Early Pennsylvanian (Morrowan) Tyrwhitt Formation sandstones. The Todhunter may be either Early Pennsylvanian or Late Mississippian in age. The Tyrwhitt and Tobermory Formations are similar and consist mainly of brown to grey weathering, dolomitic and quartzitic, very fine-to fine-grained quartz-chert sandstone, with some thin, interbedded, locally fossiliferous, sandy dolomite beds. The Storelk Formation is quartzitic, very fine- to medium-grained, massive, cross-bedded, white weathering, quartz-chert sandstone. These formations all contain varying amounts of scattered medium and coarse sand. The Kananaskis Formation consists of sandy and cherty, dense, microcrystalline, grey dolomite.

The contact between the Storelk and Tobermory is a regionally angular unconformity. The Tobermory-Kananaskis contact is conformable and locally transitional, and the Tobermory may be in part a facies equivalent of the Kananaskis Formation. The Tyrwhitt and Storelk are Early Pennsylvanian (Morrowan) in age, and the Tobermory and Kananaskis are Middle Pennsylvanian (Atokan) in age. The Kananaskis is overlain unconformably by the Permian Ishbel clastic seiments, and towards the east successively younger strata onlap successively older strata.

The Pennsylvanian sediments may have been deposited in a structural basin between the eugeosyncline and stable platform, and individual formations thin in a northwesterly and southwesterly direction toward the supposed basin flanks where as little as 160 feet of sediments are present, whereas over 1,100 feet of equivalent strata is preserved in the central part of the basin. The strata of Chesterian and Morrowan age represent a regressive sequence. After Morrowan time, gentle warping, emergence and erosion caused truncation of Lower Pennsylvanian and Upper Mississippian strata towards the east. Regional angualr truncation, and local conglomerates composed of chert, phosphorite, sandstone and dolomite granules and pebbles mark this unconformity. Strata of Atokan age thicken westward and represent a transgressive sequence which onlaps and truncates the underlying strata.

The Pennsylvanian sandstones are a potential major source of pure silica sand.